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Dietary supplement

L-Theanine 250 mg Ingredients & Drug Interactions

by Kirkman

L-Theanine 250 mg label
See full label image
Capsule Category: Non-nutrient/non-botanical
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 30, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Theanine 250 mg against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Moderate

L-Theanine 250 mg is a dietary supplement by Kirkman with 1 active ingredient. Its ingredients are commonly taken for anxiety and stress, relaxation and calm, sleep support.Based on those ingredients, 565 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are L-Theanine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against L-Theanine 250 mg by Kirkman

Ask about any prescription or over-the-counter medication and we check it for interactions with L-Theanine 250 mg by Kirkman — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of L-Theanine 250 mg by Kirkman

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Aug 13, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

This product contains a single active ingredient: L-theanine 250 mg per capsule. L-theanine is an amino acid found in tea that works in your brain to support relaxation and mental focus.

The capsule also contains inactive ingredients — microcrystalline cellulose, hypromellose, water, and magnesium stearate — which are fillers and binders that hold the capsule together.

Does it work?

Moderate evidence
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed

This product doesn't appear to be marketed for a specific use, so we graded Theanine's overall clinical evidence instead.

Moderate

Some clinical evidence supports Theanine for:

Why this rating?
  • We looked at the product name, claims, and label statements and couldn't find a stated purpose to grade.
  • Since the label doesn't commit to one use, we graded the ingredient's overall clinical evidence instead.
  • On file: Cognitive function — rated "Possibly Effective" (Natural Medicines).

L-theanine is possibly effective for cognitive function based on available evidence. For age-related cognitive decline, Alzheimer disease, generalized anxiety disorder, obsessive-compulsive disorder, and cancer, the evidence we hold is insufficient to say whether it works or not.

The evidence, ingredient by ingredient Theanine

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

L-theanine is generally well tolerated in healthy adults for short-term use, but we don't have good long-term safety data. Some people report headaches, drowsiness, longer sleep, or more vivid dreams.

There isn't enough safety data to know whether it's okay during pregnancy or while breastfeeding — talk with your doctor or pharmacist for personalized guidance if you're pregnant, planning pregnancy, or nursing.

Side effects, ingredient by ingredient Theanine

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Theanine.
  • The most serious interaction on file is rated Moderate.
  • For scale: 565 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Check your blood pressure medications (antihypertensives) before starting — theanine may lower blood pressure further. Also confirm any sedating drugs (sleep aids, anti-anxiety meds) and serotonergic antidepressants with your doctor or pharmacist, since minor additive effects are possible.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with some supporting evidence behind its ingredients' uses. Moderate medication interactions have been identified, and safety information is well characterized.

L-theanine may help with focus and mental clarity, but the evidence is strongest for cognitive function and weaker for anxiety or neurological conditions. If you take blood pressure medication, sedatives, or serotonergic drugs like certain antidepressants, check with your doctor or pharmacist first — theanine could affect how those work.

For short-term use in otherwise healthy adults, it's generally tolerated well.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Sep 25, 2023.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about L-Theanine 250 mg, straight from the product label.

Brand Kirkman
Barcode (UPC) 812325022144
Net contents 100 Capsule(s)
Market status On market
Date entered into DSLD Sep 25, 2023
DSLD ID 297055
Product type Non-nutrient/non-botanical
Supplement form Capsule
Dietary claims / uses All Other
Intended target group(s) Adult (18 - 50 Years), Gluten Free, Dairy Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for L-Theanine 250 mg by Kirkman, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
1 Capsule(s)
Maximum serving Sizes:
2 Capsule(s)
Servings per container
100
UPC/BARCODE
812325022144
IngredientAmount% DV
L-Theanine250 mg--

Other ingredients: Microcrystalline Cellulose, Hypromellose, Water, Magnesium Stearate

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Storage

Important: Store in a cool dry place and tightly capped.

Precautions

Keep out of the reach of children.

Formulation

Free of: Milk, Eggs, Fish, Shellfish, Tree Nuts, Peanuts, Wheat or Soy

Hypoallergenic

Gluten-Free

Seals/Symbols

Ultra Tested cGMP Certified

FDA Statement of Identity

Dietary Supplement

Suggested/Recommended/Usage/Directions

Suggested Use: Take one to two capsules daily or as directed by a physician.

General Statements

503.694.1600

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

L-Theanine 250 mg by Kirkman label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

L-Theanine 250 mg label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in L-Theanine 250 mg by Kirkman

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size1 Capsule(s) Dosage formCapsule Servings per container100 Amounts shown are per serving.

L-Theanine

Interacts with
565 drugs
250 mg per serving

Theanine (usually L-theanine) is an amino acid found naturally in tea leaves that many people take to feel calmer and less stressed without strong dro...

L-Theanine monograph & interactions

Other (inactive) ingredients: Microcrystalline Cellulose, Hypromellose, Water, Magnesium Stearate. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Theanine 250 mg by Kirkman Drug Interactions

Want to check YOUR meds against L-Theanine 250 mg?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
565Drugs
172 Moderate 393 Minor

Ingredients driving the most interactions

L-Theanine 565

Individual Drug Interactions

The ingredients in L-Theanine 250 mg interact with 565 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Theanine 250 mg interact with drugs. Each result below shows which ingredient is responsible. L-Theanine

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Theanine 250 mg with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

L-Theanine3 drug types · 565 drugs

Antihypertensive Drugs

Theanine might lower blood pressure, potentiating the effects of antihypertensive drugs.
Animal research shows that theanine can lower blood pressure in spontaneously hypertensive animals. Theoretically, concomitant use of theanine and antihypertensive drugs might potentiate the antihypertensive activity.

Likelihood Possible Evidence D
Cns Depressants

Theoretically, theanine might have additive sedative effects when used in conjunction with CNS depressants. However, it is unclear if this concern is clinically relevant.
Theoretically, theanine may compete with glutamate and/or increase plasma gamma-aminobutyric acid (GABA) levels, which could cause CNS depression. In one clinical study, some subjects taking oral theanine reported drowsiness.

Likelihood Unlikely Evidence D
Serotonergic Drugs

Clinical studies regarding the effects of L-theanine on serotonin levels are conflicting. Some studies suggest it can increase serotonin levels in the brain while others report that it may decrease them. Nevertheless, there have been no reports of l-theanine being a causative agent in serotonergic-related side effects or serotonin syndrome.

Likelihood Unlikely Evidence C
L-Theanine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for L-Theanine 250 mg, from the product label.

Kirkman

See all Kirkman products
Name
Kirkman
City
Lake Oswego
State
OR
ZipCode
97035
Phone Number
(800) 245-8282
Web Address
www.kirkmangroup.com
Pharmacist Counseling Corner

L-Theanine 250 mg by Kirkman: Common Questions

Does L-Theanine 250 mg by Kirkman interact with any medications?
Yes. Based on its ingredients, L-Theanine 250 mg has a known interaction with 565 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Theanine 250 mg contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
What is L-theanine, and what's it supposed to do?
L-theanine is an amino acid that comes from tea. In this product, it's used to support relaxation and mental focus. Evidence shows it's possibly effective for cognitive function, but for anxiety and other conditions, we don't yet have enough data to confirm it works.
Can I take this if I'm pregnant or breastfeeding?
There isn't enough safety data to know either way. Talk with your doctor or pharmacist before taking it — they can weigh the risks and benefits for your situation.
What side effects might I notice?
Some people report headaches, drowsiness, longer sleep, or more vivid dreams. These aren't common, but they're the ones we know about from people who've used it.
Is this safe for long-term use?
It's generally well tolerated for short-term use in healthy adults, but we don't have solid safety data for long-term use. Talk with your pharmacist or doctor if you're thinking about taking it regularly.
Will this interact with my blood pressure medication?
Possibly. Theanine may lower blood pressure on its own, so combined with blood pressure medication, the effect could be stronger than expected. Check with your doctor or pharmacist before adding this to your routine.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Not sure if L-Theanine 250 mg is safe with your meds?

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Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

L-Theanine 250 mg label
Go deeper

The Full Monographs Behind L-Theanine 250 mg’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Theanine

Interacts with 565 drugs

Theanine (usually L-theanine) is an amino acid found naturally in tea leaves that many people take to feel calmer and less stressed without strong drowsiness. Early research suggests it may...

Read the full Theanine monograph →
Sources

Sources & How We Checked

L-Theanine 250 mg's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 6 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Theanine 6 references
  1. Yokogoshi H, Kobayashi M. Hypotensive effect of gamma-glutamylethylamide in spontaneously hypertensive rats. Life Sci 1998;62:1065-8.
  2. Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., and Scholey, A. B. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol.Psychol. 2008;77(2):113-122. PubMed
  3. Yokogoshi, H., Kato, Y., Sagesaka, Y. M., Takihara-Matsuura, T., Kakuda, T., and Takeuchi, N. Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci.Biotechnol.Biochem. 1995;59(4):615-618. PubMed
  4. Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011;16(4):348-
  5. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr 2017;29(2):72-9.
  6. Tsuchiya T, Honda H, Oikawa M, et al. Oral administration of the amino acids cystine and theanine attenuates the adverse events of S-1 adjuvant chemotherapy in gastrointestinal cancer patients. Int J Clin Oncol 2016;21(6):1085-90. PubMed

See these in context on the Theanine monograph →

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

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